1. Field of the Invention
The present invention relates to a device for suspending a payload in a launch vehicle for launching said payload into space and more particularly to a device that includes a force-absorbing system installed between first and second rigid annular members concentric with the longitudinal axis of the launch vehicle and respectively fastened to said launch vehicle and said payload and a control system for said force-absorbing system adapted to modify the stiffness of the suspension device in various phases of the flight of the launch vehicle.
2. Description of the Related Art
This kind of device is disclosed in International patent application WO 98/32658 filed by the applicant and is designed to be integrated into a launch vehicle for launching a payload into space shown diagrammatically in FIG. 1 of the accompanying drawings, in which the launch vehicle has a first stage 1 equipped with boosters 2 and 3 parallel to the longitudinal axis X of the stage and fixed to the shell of the first stage in diametrally opposite positions. FIG. 1 also shows diagrammatically a payload such as a satellite 4 mounted on a second stage 5 of the launch vehicle by means of an adapter in the form of a frustoconical skirt 6. The satellite is conventionally protected by a nose-cap 7 while it is passing through the atmosphere.
As explained in the aforementioned patent application, the thrust developed by the boosters 2, 3 applies very high forces to the shell of the first stage, in particular at the points 8, 9 where the boosters 2, 3 are attached to the first stage.
The forces are much higher at these attachment points, and if they were transmitted to the skirt 6 they would deform it asymmetrically, which could damage the satellite if countermeasures were not applied. According to the aforementioned patent application, the countermeasures consist of installing a suspension device which takes the form of an annular chamber with flexible walls arid filled with a fluid between the satellite and the launch vehicle, for example at the level of the larger base 6b of the skirt 6, whose other base 6a receives the satellite. The xe2x80x9cexcessxe2x80x9d forces exerted on the annular chamber in line with the attachment points 8, 9 are uniformly distributed in the circumferential direction by the fluid in the chamber and the skirt 6 is therefore subjected to perfectly symmetrical forces that do not deform it asymmetrically. This maintains the integrity of the satellite when the boosters 2, 3 are operating.
Means are provided for varying the pressure of the fluid in the annular chamber. The pressure can be reduced from a relatively high value ensuring good mechanical cohesion of the launch vehicle and the skirt 6, which is necessary in particular when the boosters 2, 3 are operating, to a lower value for absorbing and damping forces such as vibration or shock propagating in the launch vehicle, in particular on separation of the stages of the launch vehicle and the nose-cap 7.
The device described in the patent application previously cited achieves the stated objectives. However, it implies the use of either a flexible wall annular chamber or a chamber with two complementary rigid annular walls that are axially mobile relative to each other and sealed by at least one O-ring whose length is equal to the circumference of the chamber.
Because it is integrated into a launch vehicle, this kind of device must be very reliable. Making it very reliable can be very costly because of sealing problems caused by using a flexible wall annular chamber or an annular chamber incorporating an O-ring with the same circumference.
If the flexible wall annular chamber solution is adopted, when the pressure in the chamber is high the flexible wall is greatly stiffened, to the point that forces transmitted by the device pass through the wall, rather than through the fluid it confines, which renders the device ineffective at high pressures.
An object of the present invention is precisely to provide a device for suspending a payload in a launch vehicle for launching said payload into space which is free of the above drawbacks and which in particular enables the stiffness of the suspension to be varied to adapt it to particular conditions encountered during successive phases of the flight of the launch vehicle, combined with high reliability and moderate production cost.
To be more precise, an object of the invention is to provide this kind of device adapted to have a relatively higher stiffness during ordinary phases of the flight of the launch vehicle, to confer good mechanical cohesion thereon, and a relatively lower stiffness during extraordinary phases of the flight of the launch vehicle, such as those corresponding to separation of the nose-cap or of stages of the launch vehicle, which phases generate shock and/or vibration which must be absorbed or damped before it propagates as far as the satellite.
The above objects of the invention, together with others that will become apparent on reading the following description, are achieved by means of a device for suspending a payload in a launch vehicle for launching said payload into space, the device including elastic force-absorbing means installed between first and second rigid annular members concentric with a longitudinal axis of the launch vehicle and respectively fastened to said payload and said launch vehicle, and control means for controlling said elastic force-absorbing means suitable for adapting the stiffness of the suspension device to various phases of the flight of the launch vehicle, characterized in that said control means include a plurality of hydraulic thrust bearings between said first and second rigid annular members, said thrust bearings being mobile between a first position in which they couple said annular members rigidly and a second position in which said elastic force-absorbing means are activated.
As shown in more detail later, the resulting flexibility of the payload suspension can filter shock occurring during the extraordinary phases of flight mentioned above.
In accordance with the invention, the stiffness of the suspension device is varied by appropriately controlling conventional hydraulic thrust bearings which can be sealed to the level of reliability required by the aerospace industry at moderate cost.
According to other features of the device according to the invention, said elastic force-absorbing means consist of a plurality of spring thrust bearings, said plurality of spring thrust bearings and said plurality of hydraulic thrust bearings being interleaved with each other. The hydraulic thrust bearings are at equal pressures. The control means include a circuit for feeding said hydraulic thrust bearings with liquid and said circuit includes a cylinder for selectively varying the pressure of said liquid between first and second values controlling the placing of the hydraulic thrust bearings in their first and second positions, respectively.